Hybrid type powertrains generally employ an internal combustion engine and one or more motor/generator units that operate in concert to provide driving power to the wheels of a vehicle. The electric drive capability of the vehicle is generally used where noise or exhaust emissions are of prime concern. This type of vehicle is suited, by way of example, for operation in a closed environment (electric drive), such as a passenger terminal, and an open environment (engine drive) such as a highway. Thus the vehicle is ideal for transporting passengers from a terminal to their destinations.
Vehicles employing a hybrid powertrain are also well suited for urban transportation where a significant amount of stop and go driving is undertaken. These vehicles use electrical regenerative braking to recharge the electrical power storage devices (batteries). During urban travel the powertrain takes advantage of both the internal combustion engine and the electric drive to improve both fuel economy and exhaust emissions. The hybrid powertrain permits the engine to be shut-off at vehicle stops. The electric drive may be used for engine restart and/or vehicle acceleration.
The hybrid powertrains are also suited for over-the-road transportation where the electric drive units can be utilized to assist in driving the vehicle during high-power output conditions such as rapid acceleration and hill climbing. The electric drive units might also provide propulsion in the event that engine operation is inadvertently discontinued. Also the powertrains generally include planetary gearing which is designed to effectively combine the electrical and mechanical drive units into an integrated system.
So-called Flywheel-Alternator-Starter (FAS) systems position the electric drive between the engine and the transmission. These systems may increase the transmission size longitudinally and radially.
U.S. Pat. No. 6,208,036, commonly owned with the present application and hereby incorporated by reference in its entirety, provides a hybrid powertrain with an engine, a power transmission, and an electric drive (motor/generator). A torque converter is positioned between the engine and a planetary gear arrangement, and the rotor of the motor/generator is secured to the outer periphery of the torque converter. The stator of the motor/generator is secured within the housing assembly surrounding both the rotor and the torque converter.